1. Technical Field of the Invention
The present invention relates to a magnetic data processing device, a magnetic data processing method and a magnetic data processing program, and more particularly to a technology for determining the reliability of magnetic data.
2. Description of the Related Art
Conventionally, a magnetic sensor has been used to measure orientation or the like. When magnetism is measured using a magnetic sensor, the output of the magnetic sensor includes not only components of a measurement target such as Earth's magnetism (geomagnetism) but also noise or offset components. For example, in the case where Earth's magnetism is measured by a magnetic sensor in a Personal Navigation Device (PND) mounted in a transportation device such as a vehicle, the offset component is caused by magnetization of the transportation device or the PND itself, or is caused by temperature characteristics of the magnetic sensor. The offset component varies as operating environments such as magnetization of the vehicle or temperature vary. Therefore, the output of the magnetic sensor is corrected by subtracting an offset component derived based on the output of the magnetic sensor from the output of the magnetic sensor (for example, see Patent Reference 1).
[Patent Reference 1] Japanese Patent Application Publication No. 2007-240270
However, in the case where Earth's magnetism is measured by a magnetic sensor in a PND mounted in a transportation device, the offset component is caused by a magnetic field generated by an electronic circuit mounted in the transportation device or the PND or is caused by a magnetic field that the transportation device receives when traveling near a strong magnetic field source such as a grade crossing. Accordingly, it is difficult to perform the correction for perfectly negating the noise component. Therefore, in a system using such a magnetic sensor, an error is included in data derived from the output of the magnetic sensor. However, when the output of the magnetic sensor contains a great error or when an error in one magnetic data element is amplified by an error in another magnetic data element, the reliability of the system is significantly hampered. Thus, it is important to determine the reliability of magnetic data output from the magnetic sensor.